
<html>
<head>
    <title>NeHe's Lesson 11 for WebGl (Flag Effect (Waving Texture))</title>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
    <style type="text/css">
        canvas {
            border: 2px solid black;
            -moz-box-shadow: black 2px 2px 2px;
            background-color: black;
        }
    </style>
    <script src="http://derekliu.blog.51cto.com/attachment/201205/4479510_1337314020.jpg" type="text/javascript"></script>
    <script src="http://derekliu.blog.51cto.com/attachment/201205/4479510_1337314011.jpg" type="text/javascript"></script>

    <!-- Fragment shader program -->

    <script id="shader-fs" type="x-shader/x-fragment">
        varying highp vec2 vTextureCoord;

        uniform sampler2D uSampler;

        void main(void) {
        gl_FragColor = texture2D(uSampler, vec2(vTextureCoord.s, vTextureCoord.t));
        }
    </script>

    <!-- Vertex shader program -->

    <script id="shader-vs" type="x-shader/x-vertex">
        attribute highp vec3 aVertexPosition;
        attribute highp vec2 aTextureCoord;

        uniform highp mat4 uNormalMatrix;
        uniform highp mat4 uMVMatrix;
        uniform highp mat4 uPMatrix;

        varying highp vec2 vTextureCoord;

        void main(void) {
        gl_Position = uPMatrix * uMVMatrix * vec4(aVertexPosition, 1.0);
        vTextureCoord = aTextureCoord;
        }
    </script>
</head>

<body>
<canvas id="glcanvas" width="640" height="480">
    Your browser doesn't appear to support the HTML5 <code>&lt;canvas&gt;</code> element.
</canvas>
<script type="text/javascript">
var canvas;
var gl;

var cubeVerticesBuffer;
var cubeVerticesTextureCoordBuffer;
var cubeVerticesIndexBuffer;
var cubeVerticesNormalBuffer;
var cubeRotation = 0.0;
var lastCubeUpdateTime = 0;

var cubeImage;
var cubeTexture;

var mvMatrix;
var shaderProgram;
var vertexPositionAttribute;
var vertexNormalAttribute;
var textureCoordAttribute;
var perspectiveMatrix;

var points=[];
var xrot=0.0,yrot=0.0,zrot=0.0;
var wiggle_count = 0;

start();
//
// start
//
// Called when the canvas is created to get the ball rolling.
//
function start() {
    canvas = document.getElementById("glcanvas");

    initWebGL();      // Initialize the GL context

    // Only continue if WebGL is available and working

    if (gl) {
        gl.clearColor(0.0, 0.0, 0.0, 1.0);  // Clear to black, fully opaque
        gl.clearDepth(1.0);                 // Clear everything
        gl.enable(gl.DEPTH_TEST);           // Enable depth testing
        gl.depthFunc(gl.LEQUAL);            // Near things obscure far things

        // Initialize the shaders; this is where all the lighting for the
        // vertices and so forth is established.

        initShaders();

        // Here's where we call the routine that builds all the objects
        // we'll be drawing.

        initPoints();
        initBuffers();

        // Next, load and set up the textures we'll be using.

        initTextures();

        // Set up to draw the scene periodically.

        setInterval(drawScene, 15);

        document.addEventListener( 'keydown', onDocumentKeyDown, false );
    }
}

//
// initWebGL
//
// Initialize WebGL, returning the GL context or null if
// WebGL isn't available or could not be initialized.
//
function initWebGL() {
    gl = null;

    try {
        gl = canvas.getContext("experimental-webgl");
    }
    catch(e) {
    }

    // If we don't have a GL context, give up now

    if (!gl) {
        alert("Unable to initialize WebGL. Your browser may not support it.");
    }
}

function initPoints(){
    for(var x=0; x<45; x++) {
        points[x] = [];
        for(var y=0; y<45; y++) {
            points[x][y] = [];
            points[x][y][0]=x/5.0-4.5;
            points[x][y][1]=y/5.0-4.5;
            points[x][y][2]=Math.sin((((x/5.0)*40.0)/360.0)*Math.PI*2.0);
        }
    }
}
//
// initBuffers
//
// Initialize the buffers we'll need. For this demo, we just have
// one object -- a simple two-dimensional cube.
//
function initBuffers() {
    var vertices = [];
    var textureCoordinates = [];
    var cubeVertexIndices = [];
    var float_x,float_y,float_xb,float_yb;
    var i=0,j=0,k=0,t=0;
    for(var x = 0; x < 44; x++ ) {
        for(var y = 0; y < 44; y++ ) {
            float_x = x/44.0;
            float_y = 1-y/44.0;
            float_xb = (x+1)/44.0;
            float_yb = 1-(y+1)/44.0;

            textureCoordinates[i]   = float_x;
            textureCoordinates[i+1] = float_y;
            vertices[j]    = points[x][y][0];
            vertices[j+1]  = points[x][y][1];
            vertices[j+2]  = points[x][y][2];

            textureCoordinates[i+2] = float_x;
            textureCoordinates[i+3] = float_yb;
            vertices[j+3]  = points[x][y+1][0];
            vertices[j+4]  = points[x][y+1][1];
            vertices[j+5]  = points[x][y+1][2];

            textureCoordinates[i+4] = float_xb;
            textureCoordinates[i+5] = float_yb;
            vertices[j+6]  = points[x+1][y+1][0];
            vertices[j+7]  = points[x+1][y+1][1];
            vertices[j+8]  = points[x+1][y+1][2];

            textureCoordinates[i+6] = float_xb;
            textureCoordinates[i+7] = float_y;
            vertices[j+9]  = points[x+1][y][0];
            vertices[j+10] = points[x+1][y][1];
            vertices[j+11] = points[x+1][y][2];

            cubeVertexIndices[k] = t;
            cubeVertexIndices[k+1] = t+1;
            cubeVertexIndices[k+2] = t+2;
            cubeVertexIndices[k+3] = t;
            cubeVertexIndices[k+4] = t+2;
            cubeVertexIndices[k+5] = t+3;

            i=i+8;
            j=j+12;
            k=k+6;
            t=t+4;
        }
    }

    cubeVerticesBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, cubeVerticesBuffer);
    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(vertices), gl.STATIC_DRAW);

    cubeVerticesTextureCoordBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ARRAY_BUFFER, cubeVerticesTextureCoordBuffer);
    gl.bufferData(gl.ARRAY_BUFFER, new Float32Array(textureCoordinates), gl.STATIC_DRAW);

    cubeVerticesIndexBuffer = gl.createBuffer();
    gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, cubeVerticesIndexBuffer);
    gl.bufferData(gl.ELEMENT_ARRAY_BUFFER, new Uint16Array(cubeVertexIndices), gl.STATIC_DRAW);
}

//
// initTextures
//
// Initialize the textures we'll be using, then initiate a load of
// the texture images. The handleTextureLoaded() callback will finish
// the job; it gets called each time a texture finishes loading.
//
function initTextures() {
    cubeTexture = gl.createTexture();
    cubeImage = new Image();
    cubeImage.crossOrigin = "";
    cubeImage.onload = function() { handleTextureLoaded(cubeImage, cubeTexture); }
    cubeImage.src = "http://derekliu.blog.51cto.com/attachment/201205/4479510_1337583348.png";
}

function handleTextureLoaded(image, texture) {
    gl.bindTexture(gl.TEXTURE_2D, texture);
    gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, gl.RGBA, gl.UNSIGNED_BYTE, image);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MAG_FILTER, gl.LINEAR);
    gl.texParameteri(gl.TEXTURE_2D, gl.TEXTURE_MIN_FILTER, gl.LINEAR_MIPMAP_NEAREST);
    gl.generateMipmap(gl.TEXTURE_2D);
    gl.bindTexture(gl.TEXTURE_2D, null);
}

//
// drawScene
//
// Draw the scene.
//
function drawScene() {
    // Clear the canvas before we start drawing on it.

    gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);

    // Establish the perspective with which we want to view the
    // scene. Our field of view is 45 degrees, with a width/height
    // ratio of 640:480, and we only want to see objects between 0.1 units
    // and 100 units away from the camera.

    perspectiveMatrix = makePerspective(45, 640.0/480.0, 0.1, 100.0);

    loadIdentity();

    mvTranslate([0.0,0.0,-12.0]);

    mvRotate(xrot,[1.0,0.0,0.0]);
    mvRotate(yrot,[0.0,1.0,0.0]);
    mvRotate(zrot,[0.0,0.0,1.0]);

    // Draw the cube by binding the array buffer to the cube's vertices
    // array, setting attributes, and pushing it to GL.

    gl.bindBuffer(gl.ARRAY_BUFFER, cubeVerticesBuffer);
    gl.vertexAttribPointer(vertexPositionAttribute, 3, gl.FLOAT, false, 0, 0);

    // Set the texture coordinates attribute for the vertices.

    gl.bindBuffer(gl.ARRAY_BUFFER, cubeVerticesTextureCoordBuffer);
    gl.vertexAttribPointer(textureCoordAttribute, 2, gl.FLOAT, false, 0, 0);

    // Specify the texture to map onto the faces.

    gl.activeTexture(gl.TEXTURE0);
    gl.bindTexture(gl.TEXTURE_2D, cubeTexture);
    gl.uniform1i(gl.getUniformLocation(shaderProgram, "uSampler"), 0);

    // Draw.
    gl.bindBuffer(gl.ELEMENT_ARRAY_BUFFER, cubeVerticesIndexBuffer);
    setMatrixUniforms();
    gl.drawElements(gl.TRIANGLES, 11611, gl.UNSIGNED_SHORT, 0);

    if( wiggle_count == 2 ) {
        for(var y = 0; y < 45; y++ ) {
            var hold=points[0][y][2];
            for(var x = 0; x < 44; x++) {
                points[x][y][2] = points[x+1][y][2];
            }
            points[44][y][2]=hold;
        }
        wiggle_count = 0;
    }
    initBuffers();
    wiggle_count++;

    xrot+=0.3;
    yrot+=0.2;
    zrot+=0.4;

    // Update the rotation for the next draw, if it's time to do so.

    var currentTime = (new Date).getTime();
    lastCubeUpdateTime = currentTime;
}

function onDocumentKeyDown ( event ) {
    //event.preventDefault();

}

//
// initShaders
//
// Initialize the shaders, so WebGL knows how to light our scene.
//
function initShaders() {
    var fragmentShader = getShader(gl, "shader-fs");
    var vertexShader = getShader(gl, "shader-vs");

    // Create the shader program

    shaderProgram = gl.createProgram();
    gl.attachShader(shaderProgram, vertexShader);
    gl.attachShader(shaderProgram, fragmentShader);
    gl.linkProgram(shaderProgram);

    // If creating the shader program failed, alert

    if (!gl.getProgramParameter(shaderProgram, gl.LINK_STATUS)) {
        alert("Unable to initialize the shader program.");
    }

    gl.useProgram(shaderProgram);

    vertexPositionAttribute = gl.getAttribLocation(shaderProgram, "aVertexPosition");
    gl.enableVertexAttribArray(vertexPositionAttribute);

    textureCoordAttribute = gl.getAttribLocation(shaderProgram, "aTextureCoord");
    gl.enableVertexAttribArray(textureCoordAttribute);
}

//
// getShader
//
// Loads a shader program by scouring the current document,
// looking for a script with the specified ID.
//
function getShader(gl, id) {
    var shaderScript = document.getElementById(id);

    // Didn't find an element with the specified ID; abort.

    if (!shaderScript) {
        return null;
    }

    // Walk through the source element's children, building the
    // shader source string.

    var theSource = "";
    var currentChild = shaderScript.firstChild;

    while(currentChild) {
        if (currentChild.nodeType == 3) {
            theSource += currentChild.textContent;
        }

        currentChild = currentChild.nextSibling;
    }

    // Now figure out what type of shader script we have,
    // based on its MIME type.

    var shader;

    if (shaderScript.type == "x-shader/x-fragment") {
        shader = gl.createShader(gl.FRAGMENT_SHADER);
    } else if (shaderScript.type == "x-shader/x-vertex") {
        shader = gl.createShader(gl.VERTEX_SHADER);
    } else {
        return null;  // Unknown shader type
    }

    // Send the source to the shader object

    gl.shaderSource(shader, theSource);

    // Compile the shader program

    gl.compileShader(shader);

    // See if it compiled successfully

    if (!gl.getShaderParameter(shader, gl.COMPILE_STATUS)) {
        alert("An error occurred compiling the shaders: " + gl.getShaderInfoLog(shader));
        return null;
    }

    return shader;
}

//
// Matrix utility functions
//

function loadIdentity() {
    mvMatrix = Matrix.I(4);
}

function multMatrix(m) {
    mvMatrix = mvMatrix.x(m);
}

function mvTranslate(v) {
    multMatrix(Matrix.Translation($V([v[0], v[1], v[2]])).ensure4x4());
}

function setMatrixUniforms() {
    var pUniform = gl.getUniformLocation(shaderProgram, "uPMatrix");
    gl.uniformMatrix4fv(pUniform, false, new Float32Array(perspectiveMatrix.flatten()));

    var mvUniform = gl.getUniformLocation(shaderProgram, "uMVMatrix");
    gl.uniformMatrix4fv(mvUniform, false, new Float32Array(mvMatrix.flatten()));

    var normalMatrix = mvMatrix.inverse();
    normalMatrix = normalMatrix.transpose();
    var nUniform = gl.getUniformLocation(shaderProgram, "uNormalMatrix");
    gl.uniformMatrix4fv(nUniform, false, new Float32Array(normalMatrix.flatten()));
}

var mvMatrixStack = [];

function mvPushMatrix(m) {
    if (m) {
        mvMatrixStack.push(m.dup());
        mvMatrix = m.dup();
    } else {
        mvMatrixStack.push(mvMatrix.dup());
    }
}

function mvPopMatrix() {
    if (!mvMatrixStack.length) {
        throw("Can't pop from an empty matrix stack.");
    }

    mvMatrix = mvMatrixStack.pop();
    return mvMatrix;
}

function mvRotate(angle, v) {
    var inRadians = angle * Math.PI / 180.0;

    var m = Matrix.Rotation(inRadians, $V([v[0], v[1], v[2]])).ensure4x4();
    multMatrix(m);
}
</script>
</body>
</html>